In my U.S. Pat. No. 3,335,630 issued Aug. 15, 1967, I describe a visual chord teaching device in which indicators visually associated with individual keys of a keyboard are controlled so as to provide an indication of a triad of keys to be manipulated in sounding a chord. These indicators are activated in response to the depression of the clavial pedal which sounds the root note of the desired triad. The device is particularly adapted to teaching the sounding of sustained chord notes as in commonly employed in playing an organ.
In my later U.S. Pat. Nos. 3,503,296 and 3,503,297, both issued Mar. 31, 1970, similar indications are obtained in response to the sounding of the root note key on the same portion of the keyboard upon which the chord is to be sounded. Again, the system is primarily directed to instruction in the sounding of sustained note chords.
Also in my U.S. Pat. No. 3,335,630 there is described a technique of fingering keys in playing chord triads identified as the 5-2-1 system.